The present invention relates to an optical switch system used, e.g., in a monitoring system for optical transmission lines including a multiplicity of optical fibers, or like systems for switching optical transmission paths.
As a method for monitoring optical transmission lines including numerous optical fibers without influencing ongoing optical communications, one illustrated in FIG. 1, for example, is known. This method is used for monitoring the optical communication lines of a system in which an electro-optic converter 2 and an opto-electric converter 3 are provided at opposite ends of optical communication lines 1 and optical signals with wavelength .lambda.1 are transmitted between the converters 2 and 3. The optical communication lines 1 include an optical multiplexer/demultiplexer 4 on the side of the electro-optic converter 2 and an optical filter 5 on the side of the opto-electric converter 3. To the optical multiplexer/demultiplexer 4 are connected optical monitoring lines 7 corresponding in number to the optical communication lines 1 and optically connected thereto. The optical monitoring lines 7 are each provided with an OTDR (optical time domain reflectometer) 6 at its end. A monitoring light beam with wavelength .lambda.2 is made to be incident sequentially to the optical monitoring lines 7 through the OTDRs 6 and is introduced into the corresponding optical communication lines 1 while being multiplexed with the optical signal with wavelength .lambda.2 by the optical multiplexer/demultiplexer 4. Only the monitoring light beam with wavelength .lambda.2 is reflected by the optical filter 5 to outside so that it is not incident to the opto-electric converter 3, while faint reflection light reflected at any points along the lengths of the fibers is transmitted back to the OTDRs 6, thereby monitoring the individual optical fibers of the optical communication lines 1.
In this method, however, the OTDR 6 which is expensive must be attached to each of the optical fibers of the optical monitoring lines 7, which is disadvantageous from the standpoint of cost and practicality.
There has been proposed another method for monitoring the individual optical fibers of optical communication lines, for example, in "1988 TohokuSection Joint Convention Record of Institutes of Electrical and Information Engineers, Japan," (Aug. 25 and 26, 1988 at Tohoku University, Department of Technology) page 140. In this method, a 1.times.n optical switch 8 is connected to the optical monitoring lines 7 and is also connected to a single OTDR 6 by means of a single optical fiber 9. The optical switch 8 serves to connect the single optical fiber 9 sequentially to the terminals of the optical monitoring lines 7.
This method, however, is disadvantageous in that the optical switch 8 requires adapters as many as the optical monitoring lines 7 to be connected thereto. The optical switch 8 therefore must necessarily be large in size if it is to be applied to large-scale optical communication lines 1. Moreover, switching or connection of the single optical fiber 9 sequentially to the terminals of the optical monitoring lines 7 requires a lot of time and labor in the case where the number of optical fibers constituting the optical monitoring lines 7 is large, for example, more than 10,000, thus making the monitoring extremely complex.